With the advance of techniques for manufacturing thin-film transistors, the liquid crystal displays (LCD) are widely applied in electrical products, such as PDAs, watches, laptops, digital cameras, mobile phones, etc. due to advantages as smaller size, portability, and lower power consumption. Further, after the industries endeavoring to research and develop new generation of manufacturing technique, the decreasing cost of production makes the TFT-LCD devices more popular and widely applied in various fields. For further promoting the quality and application of TFT-LCD devices, how to increase the wide viewing angle and shorten the response time of image are next important issues nowadays.
Please refer to FIGS. 1A and 1B, these figures show the TFT-LCD devices with multi-domain vertical alignment (MVA) developed by Fujitsu. In the associated manufacturing process, after a pixel electrode 12 is deposited on a first glass substrate 10, a bump 14 is formed thereon for controlling the alignment of liquid crystal molecules. Similarly, in the fabricating process of the color filter, another bump 16 is defined too beneath an upper glass plate 18 and a common electrode 20.
Thus, a plurality of liquid crystal molecules 22 are held between the upper and first glass substrate 18 and 10. The arrangement of liquid crystal molecules 22 without the electric field is illustrated as FIG. 1A. Some liquid crystal molecules 22 adjacent to the bump 14 and 16 are inclined slightly by the affection of bump appearance. After supplying voltage to the pixel electrode 12 and the common electrode 20, the electrical field between the upper and first glass substrate 18 and 10 is getting oblique according to the appearance of the bumps 14 and 16 to drive the liquid crystal molecules 22 rotate in the predetermined directions, as shown in FIG. 1B. Thus, the wide viewing angle, the light transmitting efficiency and the image contrast all can be increased.
Another type of MVA TFT-LCD device provided by Fujitsu is shown in FIGS. 2A and 2B. In this type of TFT-LCD device, instead of forming the bump 14 for molecule alignment, the pixel electrode 12 is etched to form an opening 15 therein. And beneath the common electrode 20, the bump 16 is still formed and disposed staggered with the opening 15. Accordingly, when there is no electric field, the liquid crystal molecules 22 are slightly inclined by affection of the bump 16 as shown in FIG. 2A. And when the pixel electrode and the common electrode are supplied with voltage, the electrical field (as dotted line) is oblique due to affection of the opening 15 and the bump 16 as shown in FIG. 2B. Due to the affections of the bump 16 and the oblique electrical field, the liquid crystal molecules 22 can rotate in the predetermined directions. It is noted that the bump 14 formed on the first glass substrate as shown in FIGS. 1A and 1B is not required in this type of TFT-LCD devices, so the step of forming the bump 14 can be omitted and the throughput can be promoted.
Please refer to FIG. 3, the TFT-LCD with back-side exposure multi-domains homeotropically aligned (BSE-MHA) developed by Industrial Research Institute of Taiwan (IRIT) is illustrated. After fabricating a pixel electrode 30 and bus-lines patterns 32 on a first glass substrate 34, surrounding wall bumps (SWB) 36 are defined on the bus-lines patterns 32, and an alignment film 37 is coated thereon. Besides, after defining a color filter 38 and a black matrix 40 beneath an upper glass plate 42, a common electrode 44 is formed beneath the color filter 38 and surrounding wall bumps 46 are next formed beneath the common electrode 44. And an alignment film 48 is then formed to cover the surrounding wall bumps 46 and the common electrode 44.
When there is no electric field, the most liquid crystal molecules 50 are vertical arranged on the right side of the dotted line in FIG. 3. However, some liquid crystal molecules 50 adjacent to the surrounding wall bump 36 and 46 are slightly inclined due to affection of the bump structures. When the pixel electrode 30 and the common electrode 44 are supplied with voltage to generate the electric field, the liquid crystal molecules 50 can rotate in predetermined directions by affections of the surrounding wall bump 36 & 46 and the oblique electrical field occurring therein to increase the brightness and the wide viewing angle as the left side of the dotted line. Notedly, no matter the MVA type or the BSE-MHA type of TFT-LCD, it is required extra procedures to form the bumps or blocks. And the associated manufacture is more complicated and the production period is prolonged.
Then please refer to FIG. 4, another type of TFT-LCD device by forming stacked bump composed of thin-film transistors is illustrated. The bumps stacked on the first glass substrate 60 include first and second bumps. The first bump comprises the stacked layers of a silicon nitride layer 62, an active layer 64, source/drain electrodes 66 and a passivation layer 68. And the second bump comprises the stacked layers of a gate structure 70, the silicon nitride layer 62 and the passivation layer 68. And a pixel electrode 72 is formed on the first glass substrate 60 between two adjacent the first bumps and on the second bump. Thus due to the affections of the bump appearance and oblique electrical field, the liquid crystal molecules can aligned in different directions to increase wide viewing angle and brightness and to shorten response time of the liquid crystal molecules.
However the associated manufacturing process is very difficult and complex because it is required to stack each layer precisely for forming the bump structures. Especially, following the promotion of the image quality, the occupied areas of the unit pixel and the thin film transistors are shrinkage, so how to deposit and align the later layer precisely onto the former layer and how to assure the gate structure and source/drain electrodes still can operate normally are both difficult.